Turns out the one spreading the rumors was Hashimoto, who did so at the behest of Sakayanagi. Shortly thereafter, Sakayanagi appears before Class C and she informs them she has evidence regarding the rumors about Ichinose.
Did Ichinose-san confess her 
past to you before today?
هل اعترفت لك إيتشينوسي-سان
بماضيها قبل اليوم؟
Hat Ichinose-san dir nicht schon vorher
von ihrer Vergangenheit erzählt?
Ichinose te confesó
lo que había hecho, ¿no?
Ichinose te confesó
lo que había hecho, ¿no?
À propos d’Ichinose.
Correggimi se sbaglio,
A Ichinose-san se confessou
para você antes de hoje?
Мне интересно…